During the dismantling of nuclear plants, such as nuclear power plants, research centers, uranium enrichment plants and reprocessing plants contaminated scraps are accumulated which, for example, fall into the category “low level radioactive waste”. These scraps may possibly be decontaminated by the remelting process and returned into the normal material cycle. Medium level contaminated scraps and high level radioactive scraps may also be accumulated. These scraps can no longer be returned into the normal material cycle and have to be disposed of in a repository. To keep costs of the repository as low as possible it is necessary to consolidate the volume of the accumulated scrap into a massive block by melting. The present invention describes a melting device and the associated method specifically tailored to this task.
During the dismantling of nuclear facilities process equipment, such as vessels, piping, fittings, meters, storage racks, linings and even metallic structural elements, such as platforms, scaffolds, stairs, etc., which are located in contaminated areas or come into contact with radioactive media have to be disposed in a repository. These components are cut during the dismantling by appropriate measures and are accumulated as a mixture of lump scrap and chips. The material is not in any case sorted, but is a mixture of different qualities, such as carbon steel, stainless steel, copper, brass, aluminum, magnesium, cadmium and others. When storing unconsolidated material many cavities would remain, which would considerably increase the repository volume and thus the costs. Furthermore, such scrap heaps provide a very large surface area, from which radionuclides could be carried off or released.
At present, for melting the scrap from nuclear plants melting devices are known which are designed as open air induction furnaces, in which the liquid melt is poured into molds. The inventors of the melting device according to the invention among others have identified the following restrictions in the solutions of the prior art:                The exhaust gases from the plants are released into the room and have to be disposed by means of a complex emission purification system.        The crucibles of these plants are made of refractory ceramic, are subjected to wear due to thermal and mechanical stress and have to be broken off after a melting campaign. In this process, the ceramic crucibles are destroyed and crushed in defined residual pieces. Thus, additionally large amounts of contaminated waste and dust are obtained as secondary waste.        The nuclear controlled area of these plants is relatively large.        Known plants are stationary plants to which the radioactively contaminated scrap has to be transported.        Scraps containing reactive metals, such as magnesium, cannot be melted.        Scrap components which develop harmful vapors, such as cadmium, can only be melted in a restrictive way.        Volatile radioactive isotopes cannot be retained.        The dismantling of such plants is very complex.        
The previously known melting facilities are all affiliated to central disposal centers where large controlled areas are established. This means that contaminated material has to be transported from the demolition site to the waste disposal centers, which increases the costs for a large transport volume of nuclear material.
DE 34 04 106 A1 describes a process for the recovery of metallic components of nuclear power plants. Disclosed is a crucible, which is introduced into the melting furnace. The melting furnace includes a furnace chamber with a furnace chamber bottom. However, the furnace is not hermetically sealed. Instead, a part of the resulting exhaust gas is sucked off by a suction hood. This melting furnace can therefore only be operated in a large safety area comprising means for preventing the contamination of the environment. Thus, the facility described therein cannot be used as a mobile unit.
DE 33 31 383 A1 describes a facility for the recovery of metallic components of nuclear power plants. The facility must be operated in a vacuum hall. Thus, the facility is neither sealed hermetically nor transportable.
Thus, numerous melting devices are known from the prior art. Common to all is that the melting devices are not transportable or are transportable only with a very large expense. Therefore, the scrap to be processed always had to be transported to the melting device. However, transports of radioactive materials are risky and regularly meet with resistance from the population.